Testing chamber



April 20, 1948. A. H. HElNEMAN 2,439,806

TESTING CHAMBER Filed Aug. 1'1, 1945 i "nl In; i "l W I| l'l FW; l

Jig E SI al "lll-ll Y 1 J Qs f Patented Apr. 20, 1948 *UNITED STATES y PATENT TESTING CHAMBER Arnold lli.` Heineman, Chicago, ill., assignor, byv

mesne assignments, to Guardite 1Gorporaton, Wilmington, Del., a corporation of lDelaware Appucauon August 11, 19,43, serial` No. 4.925.146L 4 claims. (cm3-1) This invention relates to a 'testing chamber andmore particularly` to a chamber designed for high altitude testing for aviationequipment and personnel.

One of the recent developments in aviation training and testing has been the use of testing chambers within which changes in pressure, temperature and humidity can be made in order to simulate high altitude conditions, as well as all conditions between high altitude and normal ground level atmospheric conditions. In carrying out this work it is necessary to increase and decrease the humidity with great speed, to change the temperature rapidly, as well as to change the pressure. The chambers are usually made of mild steel. This type oi steel will not withstand the low temperatures which are sometimes employed in the chambers, particularly below 50 F. It is, therefore, customary to insulate the interior of the chamber with an insulating material such as cork. In the normal changes Lwhichoccur inside of the test chamber moisture is precipitated on the walls at times which destroys the insulating value of the insulation, and removaloi the moisture from the insulation has proved dimcult.

By means of the present invention, an insulated chamber is produced in which the insulation cannot become moistened by these changes and, therefore, retains its insulating value at all times. This is done by providing an airtight metallic membrane inside the insulation and then maintaining a lower pressure within the insulation than is maintained in the chamber itself.

The invention is illustrated in the drawings in which Figure 1 represents a diagrammatic elevation of a test chamber, partly in section; and Figure 2 represents an enlarged sectional view of a portion oi the wall of the chamber.

As shown in the drawings, the chamber I has a mild steel wall II suitably braced as by beams I2, and provided with one or more doors I3. Suitable evacuation means I4 is provided for evacuating the chamber. In the drawing additional evacuation equipment I5 is shown connected to the intermediate chamber I 'I formed by the thin metallic membrane I8 and the Wall II of the chamber. The chamber II is shown as lled by an insulating material I9, preferably cork. At intervals suitable supporting means 2G may be provided which may consist of wooden stringers, but are not necessary when using an insulating material like cork. The evacuation equipment has been designated as pumps but it 2 will Ibeunderstood that these pumps may take any suitable 'Aform'including air pumps, steam jets, or any combination thereof. The chamber may nalso be provided'with an air-'inlet `2i and a steam inlet `2,2.

V*Under operating conditions the pressure within the chamber may be rapidly varied to meet test conditions. This variation may be carried out by any kind of control oi the evacuation equipment Id. The 4raising of the pressure may be controlled by operation of the valve 23 on the air line 2I andthe humidity may bel affected 'by admission of steam from the line 22 as controlled by valve 24'. Under operating-conditions all of these controls will normally be automatic, Vbut the-type of-control is no part of the present invention.

The evacuatingequipment l5 connected` to the insulation chambervl'l is shown as separate from the main evacuation equipment, but, if desired, one evacuator may be employed.

In operation there is normally a pressure be- `low which the chamber will vnot be operated,

say 2.5 to 3 inches mercury absolute. The pressure in the insulation chamber is, in accordance with this invention, normally kept at a point suitably below the normal minimum-and is always kept below the actual pressure in the test chamber. A suitable Apressure in the insulation chamber is `1.5 to -2 inches of mercury. In order that the pressure in theiinsulation chamber always be 'below the pressure in the test chamber, an automatic pressure regulator 30 of any suitable type, having pressure responsive means SI in the test chamber and 32 in the insulation chamber, is employed, to regulate the evacuation equipment I5. The pressure regulating equipment, which is available on the market and the specic structure of which is no part of this invention, is set automatically to regulate the pressure in the insulation chamber so that a suitable dilerential is maintained at all times. Thus if the pressure in the insulation chamber should rise for any reason to the extent that the predetermined differential between that pressure and the pressure in the test chamber does not exist, the evacuation equipment I5 automatically is started and the proper differential restored. As already pointed out, a differential of 1 to 1.5 inches of mercury is usually satisfactory.

In operation it is not necessary to raise the pressure within the insulation chamber beyond its normal setting when the pressure in the remainder of the chamber rises. The membrane I8 is supported against outward pressure bythe cork without deformation. Since the pressure within the insulation chamber is not permitted to rise above that in the test chamber, no inward deformation of the membrane can occur.

It is of course possible to operate the system with no pressure differential or even with a very slight positive pressure diierential between the test chamber and the insulation, chamber. Any attempt to operate in that manner, however, may cause local disturbance which will result in destruction or serious deformation of the membrane I8.

The membrane I8 may be made of any suitable airtight material. Y to be thick enough to withstand, the pressure differentials to which the wall Il is subjected, 'the` membrane may, if desired, economically be made of special steels which are not affected by the low temperatures created within the chamber.

In practice the pressure in the insulation cham ber may be Amaintained at a suiliciently low point by connecting the insulationu chamber through an automatically operated check valve 40 to the main evacuating equipment as at 4|. In this way the insulation chamber will be evacuated whenever pressure in the main evacuation line falls below the pressure in the insulation chamber. This check valve is preferably not of the ordinary spring operated type, but preferably includes independent means, not shown, for opening and closing the Valve whenever pressure in the exhaust line falls below that in the insulating chamber. Such independent means is preferred to avoid the usual leakage occurring at a check valve.

The foregoing 4detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, v Y

What I claim as new, and desire to secure by Letters Patent, is:

1. In a pressure chamber,` a pressure shell, a layer of insulating material inside the shell, an airtight membrane inside the insulation dividing the pressure chamber into an insulation chamber and a testing chamber, means for evacuating the testing chamber andthe insulation chamber to an absolute pressure near zero and for maintaining pressure in the insulation chamber at subatmospheric pressure not substantially greater than the pressure in the testing chamber, the

Inasmuch as it does not haveA pressure shell being of metal which substantially loses strength at the temperatures normally encountered in the testing chamber, and the membrane being of metal which does not substantially lose its strength at said temperatures.

A 2. In a pressure chamber, a pressure shell, a layer of solid insulation immediately inside the shell, an airtight membrane lining the inside of the insulation and forming a main testing chamber and an insulation chamber, means for evacuating the main chamber and the insulation chamber to an absolute pressure near zero and for maintaining pressure in the insulation chamber at all times below the pressure in the testing chamber, the pressure shell being of metal which substantially loses strength at the temperatures normally encountered in the testing chamber,

and the membrane being of metal which does not substantially lose its strength at said tempera- REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,787,101 Bramwell Dec. 30, 1930 2,000,882 Comstock May 7, 1935 2,026,079 White et al.Y Dee. 31, 1935 2,329,765 Jackson et al Sept. 21, 1943 FOREIGN PATENTS Number Country Date 389,535 Great Britain Mar. 23,1933 497,685 Great Britain Dec, 23, 1938 

